Lubricant for oxygen - enriched environments

ABSTRACT

A lubricating grease containing about 75 to 85% by weight of a liquid perfluoropolyether and about 15 to 25% by weight of a particulate boron nitride, preferably monomodal boron nitride having a particle size of about 7 to 10 microns; use of the lubricating grease for lubricating structures subjected to an oxygen-enriched environment and devices containing such lubricated structures.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in the lubrication ofstructures located within an oxygen-enriched environment, theformulation of greases based on high molecular weight perfluoropolyetheroils for use in oxygen-enriched environments, and structures to besubjected to an enriched oxygen environment which have been lubricatedby the perfluropolyether grease described herein.

The prior art describes a number of lubrication formulations based onfluorinated oils, including liquid perfluoropolyethers. When compoundedas grease compositions, these fluorinated oils, includingperfluoropolyethers, can be thickened with organic thickeners such aspoly(tetrafluoroethylene) and with inorganic thickeners such as aluminumnitride, boron nitride and silicon carbide. Whether as oils or greases,compositions based on perfluoropolyethers are characterized hightemperature stability, excellent resistance to chemicals and oxidizers,good lubricating properties and wide compatibility with materials ofconstruction such as plastics, metals and elastomers.

U.S. Pat. No. 7,838,475 discloses a composition that comprises an arylperfluoropolyether, optionally a halogenated oil, and further optionallya thickening agent. The composition can be used as a lubricant itself oras an additive to an oil or grease lubricant and can withstand hightemperatures without decomposition. The halogenated oil can be aperfluoropolyether, a fluorosilicone, a polytrifluorochloroethylene, orcombinations of two or more thereof The thickening agent can be finelydivided silica, boron nitride, clay, soap, poly(tetrafluoroethylene),talc, silica, titanium dioxide, polyurea, polyurethane, or combinationsof two or more thereof.

U.S. Pat. No. 7,709,424 discloses a lubricating oil composition, whichcomprises a perfluoropolyether base oil and a fluorine-containingpolyether diphosphonic acid ester, and a grease composition whichfurther contains a thickening agent in addition to the lubricating oilcomposition. The composition may include solid lubricants such asmolybdenum disulfide, graphite, boron nitride, silane nitrides, etc.

U.S. Pat. No. 7,544,646 discloses a method of lubricating a sootblowercomprising use of an oil or grease that is resistant to thermaloxidation. By “resistant to thermal oxidation” is meant that the oil orgrease can withstand temperatures less than 300 degrees centigrade foran indefinite time, that is, without thermally or oxidativelydegradating. This characteristic is distinct from use within the highlyoxygen enriched environments contemplated by the present invention. Asootblower employs air, steam or water under high pressure. The oil orgrease of the '646 patent can be an ester, silicone, or halogenated oilor grease including perfluoropolyether or perfluoroalkyl ether, afluorosilicone, a polytrifluorochloroethylene, derivatizedperfluoropolyethers, such as fluoroether triazines, and mixtures of twoor more thereof. The composition may comprise a thickening agent such aspoly(tetrafluoroethylene), boron nitride, talc, silica, metal soaps,polyurea and so on.

U.S. Pat. No. 7,265,080 discloses a rolling bearing to be incorporatedin the compressor for a fuel cell system including a fluorine-basedgrease containing a fluororesin and a fluorine-based oil, a urea greasecontaining a urea compound and a synthetic oil, or a lithium complexgrease containing a lithium complex and a synthetic oil encapsulatedtherein. Perfluoroalkylether may be the base oil, polytertafluroethylenemay be the thickening agent and various extreme pressure agents, such asorganic metal compounds including organic molybdenum compounds, organiczinc compounds, organic antimony compounds and so on, or halogen-basedextreme pressure agents, or solid lubricants including molybdenumdisulfide, tungsten disulfide, graphite, boron compounds, e.g. boronnitride, etc. are used in the lubricant compositions of the '080 patent.

U.S. Pat. No. 7,232,932 discloses a perfluoropolyether possessingimproved heat stability and which comprises perfluoroalkyl radical endgroups. Greases containing the new perfluropolyether can includestandard thickeners such as poly(tetrafluoroethylene), fumed silica andboron nitride and combinations thereof.

U.S. Pat. No. 6,632,780 discloses a highly thermal conductive greasecomposition which comprises from 70 to 90% by volume of an inorganicpowder which is a mixture containing at least two kinds of inorganicpowders different from each other in each average particle size, andfrom 10 to 30% by volume of a base oil containing a mineral oil or asynthetic oil. The mixture of inorganic powders includes zinc oxide,magnesium oxide, titanium oxide, aluminum nitride, aluminum oxide,silicon carbide, boron nitride, etc. The base oils can be numeroushydrocarbon oils such as polyol esters, polyphenyl ethers, alkylphenylethers or trimellitic acid esters, or at times can be liquidsilicone oils or fluorohydrocarbon oils such as chlorofluorocarbon andperfluoropolyethers.

U.S. Pat. No. 6,528,457 discloses a composition that can be used aslubricant for a high electric field including spark plug boots. Thecomposition comprises, or is produced by combining, a halogenated oilsuch as a perfluoropolyether, a polytrichlorofluoroethylene, afluorosilicone, or combinations of two or more thereof; a basicthickener; and optionally an additional thickener in which the basicthickener is a metal hydroxide, a metal salt, an ammonium salt, orcombinations of two or more thereof. The optional additional thickeneris polytetrafluoroethylene, talc, silica, clay, boron nitride, metalsoaps, titanium dioxide, polydimethylsiloxane, polyurea, polyurethane,or combinations of two or more thereof.

U.S. Pat. No. 6,432,887 discloses a rolling device utilizing as alubricant, among others, a composition containing a mixture of a liquidfluorinated polymer oil having a specific kinetic viscosity as a baseoil and a thickening agent, wherein the liquid fluorinated polymer oillubricant may be, for example, perfluoropolyether, telomer oftrifluoroethylene and fluorosilicone polymer, and in which thethickening agent can be a solid fluoroinated polymer, layered mineralpowder (such as powders of mica series mineral, a vermiculite mineral,and a montmorillonite series mineral each having a layered crystalstructure or a hexagonal system boron nitride), or ultra fine particlesand white nonmetal powder.

U.S. Pat. No. 6,040,277 discloses grease compositions that are resistantto high temperatures and oxidative or chemically aggressiveenvironments, containing a liquid fluorinated polymer (representativeexamples of which include telomers of chlorofluoroethylene,fluorosilicone polymers and perfluoropolyethers) and a thickening agentcontaining hexagonal lattice boron nitride powder preferably having abimodal particle size distribution (between 25 and 75 weight percenthaving an average particle size of 2 to 50 micrometers and between 75and 25 weight percent having an average particle size of 0.01 to 1micrometers) and optionally containing a solid fluorinated polymerthickening agent (such as polytetrafluoroethylene). In an Example and inComparative Examples, when the optional thickening agent is present, theboron nitride powder is described as an aggregate powder having anaverage particle size of 5 to 15 microns. As with U.S. Pat. No.7,544,646, discussed above, the skilled artisan would understandoxidative environment herein to mean high temperatures and/or pressureswhich can cause oxidative degradation of the liquid fluoroinated polymeras opposed to the enriched oxygen environment involved with theinvention of the present application.

US 2008/0028969 discloses an image forming device comprising twocomponents capable of relative movement and a lubricant disposed betweensuch components. The lubricant may include any polymeric type carriermedium such as fluorinated oils (perfluoropolyether) and silicone oils,and hexagonal boron nitride with average particle size between 0.1 and10 microns, for example an average particle size of 0.3 to 0.7 microns,capable of reducing friction between the components.

US 2010/0222244 discloses lubricating compositions based onperfluoropolyethers. More specifically, this publication discloses asolid polymer containing at least one aromatic ring that is used as anadditive to stabilize fluorinated lubricants, preferablyperfluoropolyether oils, at high temperatures, which compositions alsoinclude known thickening agents such as poly(tetrafluoroethylene), talc,silica and boron nitride.

EP 0982392 discloses a grease composition for use in, e.g., asemiconductor device to remove heat from electronic parts, having highthermal conductivity and excellent heat dissipation ability, comprising(A) 100 parts by weight of a base oil such as silicone oils andfluoroinated hydrocarbon oils (such as perfluoropolyethers and others)and (B) 500 to 1,200 parts by weight of metallic aluminum powder, and asan additional component, zinc oxide and/or boron nitride.

EP 0939115 discloses a thermally conductive grease compositioncomprising (A) 100 weight parts of at least one base oil selected fromliquid silicones, liquid hydrocarbons or fluorohydrocarbon oils such asperfluoropolyethers and 500-1,000 weight parts of a thermally conductivefiller mixture which is constituted of (B) an inorganic filler havingMohs hardness of at least 6 and thermal conductivity of at least 100 W/m° K such as aluminum nitride powder and (C) an inorganic filler havingMohs hardness of at most 5 and thermal conductivity of at least 20 W/m °K such as hexagonal boron nitride powder or zinc oxide powder.

Even with the state of the art as now exists with perfluoropolyetherlubricants, a need still exists for lubricants tailored to withstand thesevere operating conditions imposed by high oxygen-containing fluidsused in many specialized devices, such as hyperbaric medical devices andmilitary devices, and processes for lubricating the internal parts ofsuch devices. Also, a need exists for providing devices internallypressurized with a high oxygen-containing fluid, and containing improvedinternal lubrication of surfaces and structures.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process forlubricating structures, such as bearings, gears, seals, chains, shafts,etc., subjected to a continuous or intermittent oxygen-enrichedenvironment.

Another object of the present invention is to provide greaseformulations usable in processes for lubricating structures subjected toa continuous or intermittent oxygen-enriched environment.

Still another object of the invention is to provide grease formulationswhich can be used in processes for lubricating internal structureswithin a pressurized oxygen environment.

A further object of this invention is to provide devices comprising apartially or fully enclosed area subjected to an oxygen enriched gas andcontaining internal structures such as bearings, gears, seals, chains,shafts, etc., lubricated with the grease disclosed herein.

Other objects of the present invention will be apparent to the skilledartisan from the detailed description of the invention hereinafter.

In accordance with the present invention, a process has now been foundfor lubricating structures subjected to an oxygen enriched fluid whichcomprises lubricating such structures with a grease comprising a highmolecular weight perfluoropolyether and a particulate boron nitride ofdefined particle size. More particularly, it has now been found thatstructures internal to a device subjected to a continuous or anintermittent oxygen-enriched fluid can be lubricated without breakdownof the lubricant by using a lubricating grease comprising a highmolecular weight perfluoropolyether and a boron nitride having aparticle size of 1 to 20 microns, especially a 7 to 10 micron particlesize. The lubricating grease used in the present invention comprisesabout 70 to 90 percent by weight of the high molecular weightperfluoropolyether and about 10 to 30 percent by weight of theparticulate boron nitride, more particularly, about 75 to 85 percent byweight of the perfluoropolyether and about 15 to 25 percent by weight ofthe boron nitride. The devices lubricated in accordance with the presentinvention, even when exposed to an oxygen enriched environment oratmosphere approaching or at essentially 100% oxygen content, arecharacterized by an extended useful life, all other factors beingconstant, and especially as compared with conventional lubrication ascarried out in the prior art.

In preferred embodiments of the present invention, novel devices to besubjected to a continuous or intermittent oxygen enriched atmosphere, orinternally pressurized by an oxygen enriched atmosphere, are provided.These devices include internal structures lubricated with a greasecomprising about 75 to about 85 percent by weight high molecular weightperfluoropolyether and about 15 to 25 percent by weight of particulateboron nitride having a particle size of about 7 to about 10 microns. Ina more preferred embodiment of the present invention, the particulateboron nitride is monomodal boron nitride having a particle size of 7 to10 microns.

In preferred embodiments of the present invention, the inventive greaseconsists essentially of the high molecular weight perfluoropolyether andthe particulate boron nitride, or consists of the perfluoropolyether andthe boron nitride. Other preferred and non-preferred embodiments of thepresent invention will be obvious to the skilled artisan from thedetailed description of the invention hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to improving the internal lubricationof devices which in use are subjected to an oxygen enriched environment.Such devices are well known and include gaskets, actuators, regulators,valves and valve packings. They range in use from ventilators, oxygenconcentrators, certain types of scuba and other diving equipment andmedical devices such as hyperbaric chambers to military equipment suchas internal sections of rockets through which high oxygen content gasesflow under high pressure. A representative listing of such devices,which is not exhaustive by any means, would include:

Oxygen Cylinder or Distribution Manifold Service:

Cylinder valves, pressure regulators, valve integrated pressureregulators, relief valves and check valves

Oxygen Hospital Distribution Systems (LOX and GOX):

Master/station valves, flow meters and quick connect fittings

Oxygen Ventilator/Respiratory Care Systems:

All aspects of respiratory care systems, oxygen ventilators, air/oxygensleep apnea units, oxygen conservers and oxygen concentrators

Hyperbaric and Hypobaric Chambers

By “oxygen-enriched environment” is meant a gaseous or liquid phase inwhich the oxygen content is more than 25 mol % oxygen, and is meant toinclude an oxygen content of up to essentially 100 mol % oxygen.

When less than 100 percent oxygen is present within a particular device,the remainder would be whatever content is normally employed in theparticular device. In one aspect of the present invention, wheredesired, the oxygen content within the device may be increased above itsnormal level without concern for the device's lubricated surfaces andstructures.

The grease of this invention is usable with materials and applicationsin connection with the production, storage, transportation ordistribution of oxygen, in addition to materials and applicationsinvolved with the use of oxygen

The grease involved in the present invention would have an apparentviscosity of at least about 250 poise at 20 degrees centigrade,preferably at least about 200 poise at 20 degrees centigrade, morepreferably at least about 150 poise at 20 degrees centigrade.

The first required ingredient of the grease composition with which thepresent invention is involved is a high molecular weight liquidperfluoropolyether, also known as a perfluoroalkylether. These productsare sold under the trademarks “KRYTOX” by E.I. du Pont de Nemours andCompany of Wilmington, Del., “FOMBLIN” by Solvay of Brussels and“DEMNUM” by Daikin Industries of Japan. Of course, perfluoropolyethersavailable from other sources or produced synthetically by processesknown in the art are equally applicable for the practice of the presentinvention. For use in the present invention, the perfluoropolyether hasa molecular weight of at least 1000, preferably about 1500 to 12,500,and most preferably about 3,000 to 8,000.

Thus, one group of preferred fluoroinated oils for use in the presentinvention comprises certain of the poly(hexafluoropropyleneoxide)compounds sold under the “KRYTOX” trademark. These compounds have theformula: F—(CF(CF₃)—CF₂—O)_(k)—CF₂CF₃ in which k is about 10 to 60,preferably about 40 to 60.

Another group of preferred fluorinated oils for use in the presentinvention comprises certain of the “DEMNUM” fluids which are alsopolyfluoroethercompounds, but where the central propylene moieties areof a straight chain, which compounds are of the formula:F—(CF₂CF₂CF₂—O)_(d)—CF₂CF₃ in which d is about 15 to 60, preferablyabout 30 to 60.

A third group of fluorinated oils for use in the present inventioncomprises certain of the “FOMBLIN” fluids, such as the “FOMBLIN Y” and“FOMBLIN M” fluids. “FOMBLIN Y” has the formula:CF₃O—[CF(CF₃)CF₂—O]_(m)—[CF₂—O]_(n)—CF₃ in which m+n is about 8 to 45,preferably about 20 to 45 and m/n is about 20 to 1,000, preferably about100 to 1000 and “FOMNLIN M” has the formula:CF₃O—(CF₂CF₂—O)_(p)—(CF₂—O)_(q—)CF₃ in which p+q is 40 to 180,preferably 100 to 180 and p/q is 0.5 to 2, preferably 1 to 2.

The particulate boron nitride powder must be of a defined particle sizefor the grease to possess its excellent lubricity and possess its highoxygen stability. That is, the boron nitride powder preferably has anaverage particle size of between 7 and 11 microns, preferably between 7and 10 microns. At least 95 percent, preferably at least 99 percent ofthe boron nitride particles fall within the above-stated particle sizeranges, and preferably at least 99.9 percent of the boron nitrideparticles are within a size range of 7 to 10 microns. Further, the boronnitride is composed, at least primarily, of single crystal hexagonalplatelets, which is known as hexagonal lattice boron nitride. This typeof boron nitride is known in the art and is commercially available from,among others, Momentive Performance Materials, Inc. Preferably, theboron nitride used herein consists of monomodal boron nitride having asingle crystal hexagonal platelet purity of at least 99.9 percent.

Optionally, minor amounts of conventional lubricating oil and greasecomponents may be included in the formulations of the present invention,as long as any such ingredient(s) do not adversely affect thelubricating and oxygen compatibility characteristics of the inventivegrease. Commonly found grease ingredients include dispersing agents,wetting agents, antiwear agents, anticorrosive agents and metalprotectants. Specific examples of these and other conventional greaseformulation additives are well known in the art and thus are not listedherein.

The inventive greases can be formulated by adding the selected fluids,or base oils, to a mixer followed by insertion of the mixer impeller.The impeller is fully submerged and does not touch the bottom of thecontainer. Mixing is begun by turning on the impeller at the minimumspeed while not causing splashing. Solids are periodically added withincreasing mixer speed as the blend thickens. The speed is maintained ashigh as possible while not exceeding a certain Hz. When all ingredientshave been added, mixing is allowed to continue until a uniform mix isobtained, which appears homogenous and free of visible particles. Themixer is then stopped and the impeller is removed and scrapped of excessgrease. The mixture is then blended to a grease consistency by passingit through a 3-roll mill at about 25 degrees Centigrade with the rollersset at an opening of about 0.0015 to 0.002 inch.

The final grease compositions are tested by various ASTM tests todetermine penetration, evaporation and other tests where appropriate.

The following formulation examples are illustrative of greasecompositions of this invention.

EXAMPLE 1

Several greases are prepared using the basic procedure described above.One base oil used is a linear perfluoropolyether with a viscosity ofabout 150 cSt at 20 degrees Centigrade. This product is commerciallyavailable from Solvay as Fomblin M-15. The thickener used is ultra finepowders of single-crystal hexagonal BN platelets with very high purity.In this instance, 77.6 weight percent of the fluorinated oil is added tothe mixing container, then with the mixer running, 22.4 weight percentof the boron nitride (grade HCP available from Momentive PerformanceMaterials) is added to make a product which is then milled to theconsistency of a grease. For small batches, a planetary Kitchen Aidmixer can be used; for large batches, a stationary Lightnin mixer can beused prior to the milling.

EXAMPLE 2

In other examples, the types of base oils, that is, linear and branchedperfluoropolyether oils, are used with different viscosities and blendedat different ratios with the thickener to produce greases with a rangeof penetration values.

The excellent degree of compatibility of the lubricating greases of thepresent invention with gaseous and liquid oxygen-enriched environmentsis shown by employing standard testing protocols. Gaseous oxygencompatibility of the inventive formulations has been evaluated usingtest methodologies indicated by ASTM G63, Standard Guide for EvaluatingNonmetallic Materials for Oxygen Service. The following tests have beencarried out on the inventive greases, with the test results for twocompositions prepared in accordance with the formulations of the presentinvention being indicated.

Autogeneous Ignition Temperature (AIT)

AIT is a relative indicator of a material's propensity for ignition, andis defined as the temperature at which the tested material spontaneouslyself-ignites in oxygen, and was tested according to ASTM G72-86(reapproved 2009). AIT is tested in a gaseous oxygen environmentof >99.5% O₂ at an initial pressure of approximately 1500 psig, withgraduated temperature increase of the test vessel. Three samples of twotest compositions were tested with the following results. AIT isindicated as above the temperature just below the test temperature atwhich ignition occurs, with a temperature increase of 5±1° C. per minuteat that stage of the test.

Composition 1:

Sample 1: AIT of >493° C.

Sample 2: AIT of >492° C. Sample 3: AIT of >490° C.

Composition 2:

Sample 1: AIT of >493° C.

Sample 2: AIT of >486° C.

Sample 3: AIT of >489° C.

The greases of the present invention are characterized by an AITin >99.5% oxygen concentration of at least above 400° C., preferably ofat least above 450° C. and most preferably at least above 480° C. AIT ofabout 480 degrees Centigrade is a preferred characteristic in theinventive greases.

Oxygen Index Testing (OI)

The OI is the minimum oxygen concentration in a mixture of oxygen andnitrogen that will just support candle-like combustion at ambientpressure and initially at ambient temperature. The OI is a relativeindication of a material's flammability or propensity for firepropagation and sustained burning. A modified version of the test methodof ASTM G125 was used. The ASTM standard does not include specificationsfor testing non-rigid materials such as the greases of the presentinvention. The modification consisted of using a horizontal cylinder andgas flow configuration, instead of the vertical configuration of theASTM standard. Other test parameters were consistent with the ASTMstandard. The specified mixture of oxygen and nitrogen was supplied toone end of the glass cylinder at a flow rate that produced a gasvelocity of 40±4 mm/s within the tube. The material was deemed flammableat a supplied oxygen concentration if 1) the flame propagated greaterthan 2 in. against the flow from the initial point of igniter flameimpingement or, 2) if the sample burned for more than 3 minutes. At anoxygen concentration of 100% (>99.5% oxygen), there was no sign ofignition after several attempts with the grease contained horizontallyin a ceramic boat within the cylinder.

Heat of Combustion Testing (ΔHc)

The ΔHc is an intrinsic property of a material and does not changesubstantially as pressure increases. The ΔHc of the greases of thepresent invention indicates high oxygen compatibility and low damagepotential should the grease ignite under service conditions. The ΔHc isthe quantity of heat liberated when a unit mass of material is burnedcompletely in oxygen and is measured according to ASTM D4809. It isexpressed as calories/gram. The ΔHc is an absolute value of a material'senergy release upon burning, which is an indication of its damagepotential. An automated isoperibol calorimeter is used to accuratelymeasure temperature rise and calculate the ΔHc. An average ΔHc±Standarddeviation for a grease Composition 1 as formulated according to thepresent invention 1 was 1280±30 while for a grease composition ofComposition 2, it was 1280±58. These measurements are at 99.5% oxygencontent.

The greases of the present invention are characterized by a ΔHc of nomore than about 1010 cal/g, preferably no more than about 1338 cal/g,and most preferably about 1280 cal/g, all within 99.5% oxygenconcentration.

Variations of the invention will be apparent to the skilled artisan fromthe above detailed description.

What is claimed is:
 1. A process for lubricating a structure exposed toan oxygen enriched fluid which comprises lubricating the structure witha lubricating grease comprising about 75 to 85 weight percent of a highmolecular weight liquid perfluoropolyether and about 15 to 25 weightpercent of a particulate boron nitride having a particle size of about 7to 11 microns.
 2. The process of claim 1 wherein the perfluoropolyetherhas a molecular weight of at least 1,000 and the boron nitride has aparticle size of 7 to 10 microns.
 3. The process of claim 2 wherein theboron nitride is composed primarily of single crystal hexagonalplatelets.
 4. The process of claim 3 wherein the boron nitride ismonomodal boron nitride.
 5. The process of claim 4 wherein thelubricated structure is subjected to a gaseous or liquid fluidcontaining at least about 99.5 mol percent oxygen.
 6. The process ofclaim 1 wherein the perfluoropolyether comprises a perfluoropolyether ofthe formula: F—(CF(CF₃)—CF₂—O)_(k)—CF₂CF₃ in which k is about 10 to 60.7. The process of claim 1 wherein the perfluoropolyether comprises aperflluoropolyether of the formula: F—(CF₂CF₂CF₂—O)_(d)—CF₂CF₃ in whichd is about 15 to
 60. 8. The process of claim 1 wherein theperfluoropolyether comprises a perfluoropolyether of the formulaCF₃O—[CF(CF₃)CF₂—O]_(m)—[CF₂—O]_(n)—CF₃ in which m+n is about 8 to 45and m/n is about 20 to 1,000 or of the formula:CF₃O—(CF₂CF₂—O)_(p)—(CF₂—O)_(q—)CF₃ in which p+q is 40 to 180 and p/q is0.5 to
 2. 9. The process of claim 1 wherein the grease has an autogenousignition temperature of at least about 400 degrees centigrade in >99.5%oxygen concentration.
 10. The process of claim 1 wherein the grease hasan average heat of combustion of about 1,280 calories/gram in >99.5%oxygen concentration.
 11. A device of the type which will contain acontinuously or intermittently supplied oxygen enriched atmosphere, saiddevice comprising an internal lubricated structure lubricated with thegrease of claim
 1. 12. A device of the type internally pressurized withan oxygen enriched atmosphere, said device comprising an internalstructure lubricated with the grease of claim
 1. 13. A device of thetype which will contain a continuously or intermittently supplied oxygenenriched atmosphere, said device comprising an internal lubricatedstructure lubricated with the grease of claim
 2. 14. A device of thetype internally pressurized with an oxygen enriched atmosphere, saiddevice comprising an internal structure lubricated with the grease ofclaim
 2. 15. A device of the type which will contain a continuously orintermittently supplied oxygen enriched atmosphere, said devicecomprising an internal lubricated structure lubricated with the greaseof claim
 4. 16. A device of the type internally pressurized with anoxygen enriched atmosphere, said device comprising an internal structurelubricated with the grease of claim
 4. 17. A lubricating greasecomprising about 75 to 85 percent by weight of a liquidperfluoropolyether having a molecular weight of at least 1000 and about15 to 25 weight percent of a particulate monomodal boron nitride havinga particle size of about 7 to 10 microns.
 18. The lubricating grease ofclaim 17 wherein the boron nitride is composed of single crystalhexagonal platelets.
 19. A lubricating grease consisting essentially ofabout 75 to 85 percent by weight of a liquid perfluoropolyether having amolecular weight of at least 1000 and about 15 to 25 weight percent of aparticulate monomodal boron nitride having a particle size of about 7 to10 microns.
 20. The lubricating grease of claim 19 wherein the boronnitride is composed of single crystal hexagonal platelets.
 21. Thelubricating grease of claim 19 wherein the perfluoropolyether comprisesa perfluoropolyether of the formula: F—(CF(CF₃)—CF₂—O)_(k)—CF₂CF₃: inwhich k is about 10 to
 60. 22. The lubricating grease of claim 21wherein the perfluoropolyether comprises a perflluoropolyether of theformula: F—(CF₂CF₂CF₂—O)_(d)—CF₂CF₃ in which d is about 15 to
 60. 23.The lubricating grease of claim 19 wherein the perfluoropolyethercomprises a perfluoropolyether of the formulaCF₃O—[CF(CF₃)CF₂—O]_(m)—[CF₂—O]_(n)—CF₃ in which m+n is about 8 to 45and m/n is about 20 to 1,000 or of the formula:CF₃O—(CF₂CF₂—O)_(p)—(CF₂—O)_(q—)CF₃ in which p+q is 40 to 180 and p/q is0.5 to
 2. 24. A lubricating grease consisting of about 75 to 85 percentby weight of a liquid perfluoropolyether having a molecular weight of atleast 1000 and about 15 to 25 weight percent of a particulate monomodalboron nitride having a particle size of about 7 to 10 microns.
 25. Thelubricating grease of claim 24 wherein the boron nitride is composed ofsingle crystal hexagonal platelets.
 26. The lubricating grease of claim24 wherein the perfluoropolyether comprises a perfluoropolyether of theformula F—(CF(CF₃)—CF₂—O)_(k)—CF₂CF₃ in which k is about 10 to
 60. 27.The lubricating grease of claim 24 wherein the perfluoropolyethercomprises a perflluoropolyether of the formulaF—(CF₂CF₂CF₂—O)_(d)—CF₂CF₃ in which d is about 15 to
 60. 28. Thelubricating grease of claim 24 wherein the perfluoropolyether comprisesa perfluoropolyether of the formulaCF₃O—[CF(CF₃)CF₂—O]_(m)—[CF₂—O]_(n)—CF₃ in which m+n is about 8 to 45and m/n is about 20 to 1,000 or of the formula:CF₃O—(CF₂CF₂—O)_(p)—(CF₂—O)_(q—)CF₃ in which p+q is 40 to 180 and p/q is0.5 to 2.